Method of treating atherosclerotic occlusive disease

ABSTRACT

A tack device for holding plaque against blood vessel walls in treating atherosclerotic occlusive disease can be formed as a thin, annular band of durable, flexible material. The tack device may also have a plurality of barbs or anchoring points on its outer annular periphery. The annular band can have a length in the axial direction of the blood vessel walls that is about equal to or less than its diameter as installed in the blood vessel. A preferred method is to perform angioplasty with a drug eluting balloon as a first step, and if there is any dissection to the blood vessel caused by the balloon angioplasty, one or more tack devices may be installed to tack down the dissected area of the blood vessel surface, in order to avoid the need to install a stent and thereby maintain a ‘stent-free’ environment.

This application is a continuation of U.S. patent application Ser. No.12/483,193, filed Jun. 11, 2009, which is a continuation-in-part of U.S.patent application Ser. No. 11/955,331, filed Dec. 12, 2007, now U.S.Pat. No. 7,896,911. All of the above applications are incorporated byreference herein and made a part of this specification.

TECHNICAL FIELD

This invention relates to treatment of atherosclerotic occlusive diseaseby intravascular procedures for pushing and holding plaque accumulatedon the blood vessel walls out of the way for reopened blood flow.

BACKGROUND OF INVENTION

Atherosclerotic occlusive disease is the primary cause of stroke, heartattack, limb loss, and death in the US and the industrialized world.Atherosclerotic plaque forms a hard layer along the wall of an arteryand is comprised of calcium, cholesterol, compacted thrombus andcellular debris. As the atherosclerotic disease progresses, the bloodsupply intended to pass through a specific blood vessel is diminished oreven prevented by the occlusive process. One of the most widely utilizedmethods of treating clinically significant atherosclerotic plaque isballoon angioplasty.

Balloon angioplasty is an accepted method of opening blocked or narrowedblood vessels in every vascular bed in the body. Balloon angioplasty isperformed with a balloon angioplasty catheter. The balloon angioplastycatheter consists of a cigar shaped, cylindrical balloon attached to acatheter. The balloon angioplasty catheter is placed into the arteryfrom a remote access site that is created either percutaneously orthrough open exposure of the artery. The catheter is passed along theinside of the blood vessel over a wire that guides the way of thecatheter. The portion of the catheter with the balloon attached isplaced at the location of the atherosclerotic plaque that requirestreatment. The balloon is inflated to a size that is consistent with theoriginal diameter of the artery prior to developing occlusive disease.When the balloon is inflated, the plaque is broken. Cleavage planes formwithin the plaque, permitting the plaque to expand in diameter with theexpanding balloon. Frequently, a segment of the plaque is more resistantto dilatation than the remainder of the plaque. When this occurs,greater pressure pumped into the balloon results in full dilatation ofthe balloon to its intended size. The balloon is deflated and removedand the artery segment is reexamined. The process of balloon angioplastyis one of uncontrolled plaque disruption. The lumen of the blood vesselat the site of treatment is usually somewhat larger, but not always andnot reliably.

Some of the cleavage planes created by fracture of the plaque withballoon angioplasty form dissection. A dissection occurs when a portionof the plaque is lifted away from the artery and is not fully adherentand may be mobile or loose. The plaque that has been disrupted bydissection protrudes into the flowstream. If the plaque lifts completelyin the direction of blood flow, it may impede flow or cause acuteocclusion of the blood vessel. There is evidence that dissection afterballoon angioplasty must be treated to prevent occlusion and to resolveresidual stenosis. There is also evidence that in some circumstances, itis better to place a metal retaining structure, such as stent to holdopen the artery after angioplasty and force the dissected material backagainst the wall of the blood vessel to create an adequate lumen forblood flow.

Therefore, the clinical management of dissection after balloonangioplasty is currently performed primarily with stents. As illustratedin FIG. 24A, a stent is a tube having a diameter that is sized to theartery. A stent is placed into the artery at the location of adissection to force the dissection flap against the inner wall of theblood vessel. Stents are usually made of metal alloys. They have varyingdegrees of flexibility, visibility, and different placement techniques.Stents are placed in every vascular bed in the body. The development ofstents has significantly changed the approach to minimally invasivetreatment of vascular disease, making it safer and in many cases moredurable. The incidence of acute occlusion after balloon angioplasty hasdecreased significantly with stents.

However, stents have significant disadvantages and much research anddevelopment is being done to address these issues. Stents induce repeatnarrowing of the treated blood vessel (recurrent stenosis). Recurrentstenosis is the “Achilles heel” of stenting. Depending on the locationand the size of the artery, in-growth of intimal hyperplastic tissuefrom the vessel wall in between struts or through openings in the stentmay occur and cause failure of the vascular reconstruction by narrowingor occlusion of the stent. This may occur any time after stentplacement. In many cases, the stent itself seems to incite local vesselwall reaction that causes stenosis, even in the segment of the stentthat was placed over artery segments that were not particularly narrowedor diseased during the original stent procedure. This reaction of theblood vessel to the presence of the stent is likely due to thescaffolding effect of the stent. This reaction of recurrent stenosis ortissue in growth of the blood vessel is in response to the stent. Thisactivity shows that the extensive use of metal and vessel coverage inthe artery as happens with stenting is contributing to the narrowing.The recurrent stenosis is a problem because it causes failure of thestent and there is no effective treatment. Existing treatment methodsthat have been used for this problem include; repeat angioplasty,cutting balloon angioplasty, cryoplasty, atherectomy, and even repeatstenting. None of these methods have a high degree of long-term success.

Stents may also fracture due to material stress. Stent fracture mayoccur with chronic material stress and is associated with thedevelopment of recurrent stenosis at the site of stent fracture. This isa relatively new finding and it may require specialized stent designsfor each application in each vascular bed. Structural integrity ofstents remains a current issue for their use. Arteries that areparticularly mobile, such as the lower extremity arteries and thecarotid arteries, are of particular concern. The integrity of the entirestent is tested any time the vessel bends or is compressed anywherealong the stented segment. One reason why stent fractures may occur isbecause a longer segment of the artery has been treated than isnecessary. The scaffolding effect of the stent affects the overallmechanical behavior of the artery, making the artery less flexible.Available stenting materials have limited bending cycles and are proneto failure at repeated high frequency bending sites.

Many artery segments are stented even when they do not require it,thereby exacerbating the disadvantages of stents. There are severalreasons for this. Many cases require more than one stent to be placedand often several are needed. Much of the stent length is often placedover artery segments that do not need stenting and are merely adjoiningan area of dissection or disease. Stents that are adjusted to theprecise length of the lesion are not available. When one attempts toplace multiple stents and in the segments most in need of stenting, thecost is prohibitive since installation and material is required perstent. The time it takes to do this also adds to the cost and risk ofthe procedure. The more length of artery that receives a stent that itdoes not need, the more stiffness is conferred to the artery, and themore scaffolding affect occurs. This may also help to incite thearterial reaction to the stent that causes recurrent stenosis.

SUMMARY OF INVENTION

In accordance with the present invention, a device (and related methodof deployment) for treating atherosclerotic occlusive disease comprisesa thin, annular band of durable, flexible material (a “plaque tack”)having a plurality of barbs or anchoring elements on its outer annularperiphery, which is installed intravascularly in one or more specificpositions of a plaque accumulation site. The plaque tack is dimensionedand designed to be applied with a spring force against the plaque topress and hold it against the blood vessel walls. The barbs or anchoringelements are embedded into or at least emplaced in physical contactagainst the plaque by the spring force so that the plaque tack isretained securely in position from being dislodged. The plaque tack isgenerally used after a balloon angioplasty procedure to reopen thevessel lumen for desired blood flow. The annular band of the plaque tackhas a width in the axial (length) direction of the vessel walls that isabout equal to or less than its diameter, in order to minimize theemplacement of foreign scaffolding structure in the blood vessel. One ormore tacks are applied only in positions along the length of a plaqueaccumulation site where specific holding forces are needed to stabilizethe site and/or hold pieces of plaque out of the way of blood flow. Thebarbs or anchor points of the tack(s) may be pressed with an expansionforce into the plaque and/or vessel walls by a post-installation balloonexpansion procedure.

In the present invention, the plaque tack device is designed as aminimally invasive approach to tacking loose or dissectedatherosclerotic plaque to the wall of the artery, as illustrated in FIG.24B. It may be used to treat either de novo atherosclerotic lesions orthe inadequate results of balloon angioplasty. It is designed tomaintain adequate lumen in a treated artery without the inherentdisadvantages of vascular stents. The device may also be used toadminister medications, fluid, or other treatment (“eluting”) agentsinto the atherosclerotic plaque or the wall of the blood vessel or intothe bloodstream.

The plaque tack and installation procedure may be designed in a numberof ways that share a common methodology of utilizing an expansion forceof the delivery mechanism (such as balloon expansion) and/or the springforce of a compressible annular band to enable the tack to be moved intoposition in the blood vessel, then released, unfolded or unplied toexpand to its full diametral size within the blood vessel walls.

In a preferred embodiment, the tack device comprises a thin, annularband of durable, flexible material having a plurality of barbs oranchoring points on its outer annular periphery, said annular band beingdimensioned and designed to be applied with an expansion force againstthe plaque to press and hold the plaque at an applied site of said bandagainst the blood vessel walls. Besides stabilizing the emplacement ofthe tack, the barbs play a role in tacking the plaque to the bloodvessel wall. The annular band has a length in the axial direction of theblood vessel walls that is about equal to or less than its diameter whenexpanded. In a ring or ribbon-shaped form, the annular band can have aratio of length to diameter as low as 1/100. The plaque tack device canalso have a structure for carrying medication such that it elutes abiologically active agent to the plaque to inhibit growth and/or fortreating the blood vessel wall.

For all embodiments an important parameter characterizing design of aplaque tack is the ratio: Vessel Coverage Area (C) to Total VesselSurface area (TVS), where C/TVS is less than or equal to about 60%. Thisequation can be applied to one tack device or when several spaced-aparttack devices are placed across the length of a blood vessel treatmentarea.

In another preferred embodiment, a tack device is formed with concentricside rings or mesh bands connected by longitudinal bridge members. Asadapted from a measure of Relative Metal Surface Area (RMS) compared tothe number of longitudinal segments in the device structure, an equationfor Effective Metallic Interface (EMI) may be used to compare thisembodiment of the tack device to a typical stent, as follows:

${EMI} = \frac{\left( {1 + n^{2}} \right)C}{\sum\limits_{s = 1}^{x}({lw})_{s}}$

where x is the number of sections of metal, l is an individual metalsection length, w is an individual metal section width, C is the vesselcoverage area underneath the device (lumen surface), and n is the numberof bridge members longitudinally connected between circumferentiallyoriented segments. The summation found in the denominator can beinterpreted as the total metal surface area. The preferred embodiment ofthe tack device has an EMI≤10, whereas the EMI of a typical stent wouldbe several times greater.

The present invention also encompasses the method of using the tackdevice to treat any plaque dissection in the blood vessel after balloonangioplasty by installing it with an expansion force against the plaqueto hold it against the blood vessel walls. A most preferred methodencompasses one wherein drug eluting balloon angioplasty is firstperformed, and if there is any damage, disruption, dissection, orirregularity to the blood vessel caused by the balloon angioplasty, oneor more tack devices may be used to tack down the damaged, disrupted,dissected, or irregular blood vessel surface, so as to avoid the need toinstall a stent and thereby maintain a ‘stent-free’ environment.

Other objects, features, and advantages of the present invention will beexplained in the following detailed description of the invention havingreference to the appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are schematic diagrams of a first embodiment in ribbonform for the plaque tack device of the present invention.

FIG. 2 is a side view of the first embodiment of the ribbon tack of FIG.1B in its annular shape after deployment.

FIG. 3 is a plan view of the ribbon tack of FIG. 1B in its annular shapeafter deployment.

FIGS. 4A and 4B are alternative versions of the ribbon tack of FIG. 1Bhaving stabilizing wings.

FIG. 5 is a schematic diagram of a third embodiment of flexing star tackhaving outward triangular anchor points and inward radial fingers.

FIG. 6 is a schematic diagram of a fourth embodiment of a spiral coiltack with unjoined ends that can be pulled in opposite directionshorizontally to reduce its cross-sectional diameter for insertion in theblood vessel.

FIGS. 7A-7D show alternative shapes for the flexing star tack of FIG. 5with a variety of different anchor point designs.

FIG. 8 is a photo image of the ribbon tack of FIG. 1B showing thetongues or cutout portions protruding at an angle from the metal stripwhen the tack is bent into an annular shape.

FIG. 9 is a close-up image of the anchor points of the ribbon tack ofFIG. 1B.

FIG. 10 is a photo image of the ribbon tack of FIG. 1B prior toinstallation.

FIG. 11 illustrates a pattern of capillaries formed on the tongues ofthe ribbon tack of FIG. 1B for delivering plaque-growth retardingmaterial into the plaque.

FIG. 12 is a close-up view of the capillaries formed on the tongues ofthe ribbon tack in FIG. 11.

FIG. 13 is a schematic diagram of a second embodiment of a folding ringtack having inner V-shaped segments for folding and outerinverted-V-shaped points for anchoring.

FIG. 14 is a schematic representation of the ribbon tack loaded inmultiple units on the delivery head of a catheter tube for insertioninto the blood vessel.

FIG. 15 is a detailed view of the delivery head for the ribbon tacks inFIG. 14.

FIG. 16 is a schematic representation of the folding ring tack loaded inmultiple units on the delivery head of a catheter tube with a retainerfor holding them on the sheath in compressed form.

FIG. 17 is a schematic representation showing the folding ring tackpartially deployed.

FIG. 18 is a schematic representation showing folding ring tack fullydeployed in the blood vessel.

FIG. 19A shows a fifth embodiment of a metallic mesh tack in end view,FIG. 19B shows it in side view, FIG. 19C shows the metallic mesh tack inperspective, and FIG. 19D shows a section of the metallic mesh tack in adetailed view.

FIG. 20 is a schematic representation showing multiple units of themetallic mesh tack loaded on a catheter delivery tube.

FIG. 21 is a schematic representation showing the metallic mesh tackreleased from the delivery head and fully expanded in the blood vessel.

FIG. 22 is a schematic representation the spiral coil tack loaded inmultiple units on the delivery head of a sheath and held down by aretainer cover.

FIG. 23 is a schematic representation showing the spiral coil tackreleased from the delivery head and fully expanded in the blood vessel.

FIG. 24A illustrates the use of a stent installed after angioplasty asconventionally practiced in the prior art.

FIG. 24B illustrates the use of the plaque tack installed afterangioplasty demonstrating its advantages over the prior art.

FIG. 25 shows a detailed view of a preferred embodiment of the plaquetack formed with concentric rings connected by a series of bridgingmembers.

FIG. 26 illustrates the use of multiple tack devices which are spacedapart over the length of a treatment site as compared to a typicalstent.

DETAILED DESCRIPTION OF INVENTION

In the following detailed description of the invention, certainpreferred embodiments are illustrated providing certain specific detailsof their implementation. However, it will be recognized by one skilledin the art that many other variations and modifications may be madegiven the disclosed principles of the invention. Reference for thedescription is made to the accompanying drawings, wherein like referencenumerals refer to similar parts throughout the several views.

As illustrated in FIG. 24B, the plaque tack device in the presentinvention generally comprises a thin, annular hand of durable, flexiblematerial having a plurality of barbs or anchoring elements on its outerannular periphery. The plaque tack is dimensioned diametrally and isdesigned to be applied with a spring force against the plaque to pressand hold it against the blood vessel walls. The barbs or anchoringelements are embedded into or at least emplaced in physical contactagainst the plaque by the spring force of the plaque tack. The plaquetack extends over only a small area in the axial direction of the vesselwalls, in order to minimize the amount of foreign structure placed inthe blood vessel. One or more tacks are applied only in positions alongthe length of a plaque accumulation site where specific holding forcesare needed to stabilize the site and/or hold pieces of plaque out of theway of blood flow.

The plaque tack and installation procedure may be designed in a numberof ways that share a common methodology of utilizing the spring force ofa spring-like annular band to enable the tack to be compressed, folded,or plied to take up a small-diameter volume so that it can be moved intoposition in the blood vessel on a sheath or catheter, then released,unfolded or unplied to expand to its full-diametral size within theblood vessel walls.

In the following description, five general embodiments of the plaquetack device and how to deliver it are explained in detail, referred toas: (1) ribbon tack; (2) folding ring tack; (3) flexible ring tack; (4)spiral coil tack; and (5) metallic mesh tack. All these embodiments aredelivered into the blood vessel from endovascular insertion. Thedelivery device for each involves a delivery apparatus that has somefeatures of a vascular sheath. The delivery device for each is differentand has features that are specifically designed to deliver the specifictack

Referring to FIGS. 1A and 1B, a first preferred embodiment of the plaquetack device is shown in two versions of a ribbon tack, each having alinear, flat shape like a ribbon. The version in FIG. 1A has a base end31, rows 33 of cutout tongues or apertured portions that open out aspointed barbs or anchors, and a retainer end 35. The version in FIG. 1Bhas a base end 32, single row 34 of cutout portions that open out aspointed barbs or anchors, and a retainer end 35. Each version may bemade of a material such as a corrosion-resistant metal, polymer,composite or other durable, flexible material. A preferred material is ametal having “shape-memory” (such as Nitinol) which allows it to beformed initially with an annular shape prior to forming in a linearshape, then resume the annular shape when exposed for a length of timeat internal body temperature. When the strip is deployed in the bloodvessel, it is curved into an annular shape. FIG. 2 shows the view of thestrip of material in FIG. 1B after it is curved into its preferred shapeof deployment in the blood vessel, leaving a large inner, open area 36for blood flow through it. The barbs are shown opened to outwardlypointing angles 37 due to bending forces so that they point toward thewall or surface of the blood vessel.

In a typical configuration, the ribbon tack may have a width of about0.1 to 5 mm, a diameter (when curved in annular shape) of about 1 to 10mm, a length (when extended linearly) of about 3 to 30 mm, and a barbheight from 0.01 to 5 mm. In general, the annular band of the plaquetack has a width in the axial direction of the vessel walls that isabout equal to or less than its diameter, in order to minimize theamount of foreign structure to be emplaced in the blood vessel. For tackdesigns in a ring or ribbon shape, the width/diameter ratio can be inthe range of 1/10 to 1/100.

FIG. 3 is a schematic diagram showing a top view of the ribbon tack bentinto its annular shape. FIG. 4 shows an alternative version of theribbon tack having stabilizing wings provided along its side edges foradded lateral stability when deployed in the blood vessel. FIG. 8 showsan overhead photo image of the ribbon tack with anchors protruding at anoutward angle. FIG. 9 is a close-up image of the anchors of the annularstrip. FIG. 10 is an overhead image of the metal strip extended linearlywhen at rest.

FIG. 11 illustrates a pattern of capillaries 25 that may be formed byetching the surfaces of the tongues or cutout portions for deliveringplaque-growth retarding material or other treatment agent where the tackis installed at the plaque accumulation site. FIG. 12 illustrates howthe pattern of capillaries 25 is supplied with plaque-retarding ortreatment material through a supply conduit 24. The material may beeither resident within the channels prior to insertion of the tack ortransferred from a reservoir on the inside of the annulus, through ahole to the outside of the component on the surface, into the anchoredobject, and into the tissue wall, enabling delivery of a treatment orsuch that enables additional preventative measures for retaining optimalblood flow. The forces that enable the transfer of the material from theinside of the annulus through the tree branches might be eithercapillary force or a combination of capillary and hydraulic pressure.Capillary action, capillarity, capillary motion, or wicking is theability of a substance to draw another substance into it. The standardreference is to a tube in plants but can be seen readily with porouspaper. It occurs when the adhesive intermolecular forces between theliquid and a substance are stronger than the cohesive intermolecularforces inside the liquid. The effect causes a concave meniscus to formwhere the substance is touching a vertical surface.

The array of barbs or anchor points is used for linking the annular bandof the tack with the plaque mass or blood vessel wall. The barb is madeof a sufficiently rigid material to sustain a locking relationship withthe blood vessel tissue and/or to pierce the plaque and maintain alocking relationship therewith. The barb is comprised of a head disposedon a support body. Preferably, the head and support body are integralwith each other and are constructed as a single piece. The barb mayproject at an angle of 90 degrees to the tangent of the annular band, oran acute angle may also be used.

Referring to FIG. 13, a second preferred embodiment of the plaque tackdevice is formed as a folding ring tack having inner V-shaped segmentsfor folding alternating with outer inverted-V-shaped points. TheV-shaped segments allow the ring to be radially folded to asmall-diameter volume for carriage on a deployment tube on the end ofthe sheath. At the desired position in the blood vessel, the compressedring tack is released from the deployment tube so that the ring springsout to its full diametral shape and the outward points act as barb oranchor points embedded into or pressed against the plaque. The foldingring tack is preferably made of metal wire material. Other options forthe shape of the anchors on the outer surface may be used.

Referring to FIG. 5, a third preferred embodiment of the plaque tackdevice is formed as a flexible ring tack having a pliable or hingedstructure and formed with an array of radially extending points 59 on anouter side of the ring, and an array of inner radial fingers 50. Thearray of inner radial fingers are used to displace the points to liehorizontally flat in one axial direction when the fingers and pushed inthe opposite axial direction. With the barbs or points displaced to liehorizontally flat, the flexible ring tack can be loaded on a catheterdelivery tube and held down by a cover. The fingers are then removed sothat they are not present to obscure the blood vessel when the tack isinstalled. At the desired position, the retainer cover is displaced torelease the ring tack which springs up to extend its points radiallyoutwardly for embedding into the plaque. The body of the annular ringmay have differing degrees of thickness and different designs for thefingers in the central area, such as the raised triangular anchors 59and radial fingers 50 shown in FIG. 5.

FIGS. 7A-7D show alternative shapes for the third embodiment of FIG. 5with a variety of different anchoring designs 72, 73, 78, 80. Thefingers 76, 77 for bending the points flat for insertion are includedwith any of the designs. When the fingers are removed after pre-loading,and the flexible ring tack has been deployed, the inner area 74, 75within the annular ring 79, 82 is left unobstructed.

Referring to FIG. 6, a fourth preferred embodiment of the plaque tackdevice is formed in a coil shape 64 with ends unjoined and with barbs orpoints 61 on its outer periphery. The ends are pulled longitudinally inopposite directions to flatten the annular band to a spiral shapeextending linearly so that it can be carried around or inside the lengthof a tubular sheath into the blood vessel held in place by a retainerelement. At the desired position in the blood vessel, the retainerelement is released to allow the tack to expand back to itsfull-diameter annular shape against the plaque.

FIGS. 14 and 15 show a preferred delivery method for the ribbon tackdescribed above.

Multiple flat ribbon strips 80 in linear form are arranged in parallelin an array 80 a carried on the outer surface of the delivery head 81 ofa tubular catheter 82. Each ribbon strip 80 is carried in a respectivebarrel 83 of a multi-barreled tack magazine 84 which wraps around thecatheter, as indicated in FIG. 14. The catheter has an internal pressurechamber 85 which is loaded with saline solution or CO2 gas used to ejecta ribbon strip from its barrel as it is moved by rotation of themagazine 84 in the direction RR to bring each ribbon strip in turn to anejector position (left side of the figure) in alignment with an ejectortrack 86 formed in the delivery head. Pressurized fluid from thepressure chamber 85 is used to push a mover member that ejects theribbon strip from its barrel into the ejector track 86. As shown in moredetail in FIG. 15, the ejector track 86 leads into a curved outlettunnel 87 which bends the ribbon strip towards its annular shape as thedelivery head rotates. The outlet tunnel 87 curves 90 degrees from theaxial direction of the catheter to the radial direction facing towardthe vessel walls. This curved tunnel captures the end of the ribbonpushed into the ejector track and causes the middle part of the ribbonstrip to bulge outward toward the blood vessel wall where it will laydown perpendicular to the axis of the blood vessel. The delivery head ofthe catheter rotates as part of the delivery mechanism. As the ribbon isbeing pushed out of the delivery head under hydraulic or propulsivepressure, the rotation of the delivery head allows the ribbon to be laiddown in its annular shape spanning the blood vessel walls.

A preferred delivery method for the second described embodiment of thefolding ring tack of FIG. 13 is shown in FIGS. 16, 17, and 18. Thefolding ring tack has an overall circular shape with inner V bends thatallow it to be folded in zig-zag fashion to a compressed smaller-volumeform for loading onto the delivery end of a catheter tube 92. As shownin FIG. 16, multiple units of the compressed folding ring tacks 90 arearrayed in a series on the surface of the tube. The catheter tube ishollow and lined with a fabric 91 that slides over the outer surface ofthe tube and is pulled over the end of the tube into its interior(direction of the U-shaped arrows). The fabric is made of a strong,durable material with low friction such as Teflon or Kevlar or likematerial. Multiple tacks may be loaded onto the surface of the fabriccovering the outer surface of the catheter tube. The tacks are held downin their compressed, folded form by a shell or cover 93 that istelescoped over the catheter tube and prevents early deployment of thetacks. The shell may be a transparent plastic sleeve or similarstructure having its end set back a small distance from the end of thecatheter tube. As the fabric 91 is pulled inside the tube is pulled, thecompressed tack 90 is advanced toward the end of the catheter tube. Whenthe tack reaches the end, it is released from the shell 93, and springsback to its original shape of an annular band with outer barbs the embedor are emplaced against the plaque and blood vessel walls. FIG. 17 showsthis process in action with the tack half-way deployed. The fabric 91advancing the tack 90 is being pulled into the center of the hollowdelivery tube. FIG. 18 shows the tack in place in the blood vessel afterit has been separated from the delivery catheter.

The third preferred embodiment of the flexing ring tack of FIG. 5 may bedeployed by a similar method as described above, by loading onto asimilar sliding fabric carrier which is pulled over the outer surface ofa catheter tube, with a shell sleeved over the tube for retaining thetacks from deployment until each reaches the end of the tube.

A fifth embodiment of the plaque tack in the form of a metallic meshtack is illustrated in FIGS. 19A-D, and its manner of deployment inFIGS. 20 and 21. In FIG. 19A, the metallic mesh tack is shown in endview having an annular band 100 a formed of interleaved mesh, and outerpoints or barbs 100 b. The metallic mesh tack may be laser cut or etchedout of a metal tube form or made of thin metal wire which is looped andinterleaved in a mesh that is welded, soldered, looped and/or linkedtogether into the desired mesh shape. FIG. 19B shows the metallic meshtack in side view with barbs projecting from the annular band 100 a. Thebarbs on its outward surface will contact and embed into the wall of theblood vessel. FIG. 19C shows the metallic mesh tack at rest in its fullyexpanded state in perspective view, and FIG. 19D shows a section of themetallic mesh tack in a detailed view. The mesh pattern is specificallydesigned so that it can be compressed radially inward to asmaller-volume size for loading on a catheter delivery device to beinserted into the blood vessel.

A preferred method of delivery for the metallic mesh tack is shown inFIG. 20. Multiple mesh tacks 100 are compressed to its smaller-volumesize and loaded onto the surface of a catheter delivery tube 102 in anarray 100× over a given length of the tube. As in the previouslydescribed delivery method, a cover or shell 103 is sleeved over thesurface of the tube to hold the tacks in their compressed state andprevent early deployment of the tacks. As the cover 103 is withdrawndown the length of the tube, each mesh tack in turn is released andexpands to its full-volume size. FIG. 21 shows the mesh tack 100expanded and deployed in the blood vessel.

A preferred delivery method for the fourth described embodiment of thespiral coil tack of FIG. 6 is illustrated in FIGS. 22 and 23. The coilshaped tack in FIG. 6 is formed with barbs and a band with unjoined endsthat may or may not have a taper with a varying degrees of thicknessalong its length. This design is uncoiled in its rest state and lookslike a “broken” circle. The coil tack can be compressed to a fraction ofits at-rest diameter by pulling its ends in opposite linear directionsto form a tight spiral that occupies a smaller-diameter volume so thatit can be inserted into the blood vessel. When released it can expand toseveral times the diameter of its spiral form. FIG. 22 shows multipleunits of spiral coil tacks 110 loaded in the interior of the catheterdelivery tube 112. When the tack is compressed, it occupies severalspiral turns and it spaced out longitudinally. In this case, thedelivery catheter is lined with fabric 113 slidable on its interiorsurface over the end of the tube to its outside (indicated by the pairof U-shaped arrows). As the fabric is pulled through the center of thetube, the tack is advanced toward the end of the delivery catheter. Whenthe tack reaches the end of the delivery catheter, the tack is releasedfrom the tube and re-expands to its full size to be deployed into thewall of the blood vessel. FIG. 23 shows the tack deployed in the bloodvessel.

In the embodiments described above, the preferred plaque tack device maybe made from Nitinol, silicon composite (with or without an inertcoating), polyglycolic acid, or some other superelastic material. Theanchors can have a preferred length of 0.01 mm to 5 mm. The strip ofmaterial can be created from ribbon, round or rectangular wire or asheet of material processed through photolithographic processing, laseror water cutting, chemical etching or mechanical removal of the finalshape, or the use of bottom up fabrication, for instance chemical vapordeposition processes, or the use of injection modeling, hot embossing,or the use of electro or electroless-plating. It may be fabricated frommetal, plastic, ceramic, or composite material.

The plaque tack is designed to be inherently self-aligning, i.e., itsmechanical installation can accommodate small misalignments. This servesto facilitate placing the tacks in specific locations within diseasedblood vessels. With respect to the piercing barb that has a pointedshape, it can be used to embed in objects having irregular surfaces suchas plaque or dissected or damaged artery surfaces. After deployment ofthe plaque tack, the surgeon has the option of placing an angioplastyballoon at the site of the tack and inflating the balloon to press theanchor or anchors into the wall of the blood vessel.

Plaque Tack Design Parameters

The purposes of the plaque tack described herein, as distinct fromtraditional stenting, are to reduce the amount of implanted foreignmaterial to a minimum while still performing focal treatment of theblood vessel condition so as to cause a minimum of blood vessel wallreaction and adverse post-treatment re-stenosis. The preferred plaquetack is designed to have substantially less metal coverage and/orcontact with the blood vessel surface, thereby inciting less acute andchronic inflammation. Reduced pressure of implanted material against theblood vessel wall is correlated with a lower incidence of intimalhyperplasia and better long-term patency. Substantially reduced lengthalong the axial distance of the blood vessel permits a more targetedtreatment, correlates with less foreign body coverage of the bloodvessel surface, avoids covering portions of the surface that are not inneed of coverage, and correlates with both early and late improvedpatency of blood vessel reconstructions. The plaque tack is deployedonly where needed to tack down plaque that has been disrupted by balloonangioplasty or other mechanisms. Rather than cover an entire area oftreatment, the plaque tack is placed locally and selectively, and notextending into normal or less diseased artery segments. This permits theblood vessel to retain its natural flexibility because there is aminimal to no scaffolding effect when a small profile tack is usedlocally or when even multiple tacks are spaced apart over the area oftreatment.

One important parameter for design of a plaque tack is having a tacklength to diameter (L/D)) ratio about equal to or less than 1. That is,the length of the tack along the axis of the blood vessel is about equalto or less than the diameter of the tack. The preferred plaque tack isthus shaped like an annular ring or band, whereas the typical stent isshaped like an elongated tube. The small-profile tack can thus be usedlocally for targeted treatment of disrupted regions of the blood vesselsurface with a minimum of foreign material coverage or contact. Ourtests show that a plaque tack with length/diameter ratio≤1 causes almostno biological reaction or subsequent blood vessel narrowing incomparison to a traditional stent where the length is greater than thediameter, and usually much greater. Our tests indicate that device I/D≤1results in a reduction in scaffolding much less than that of the typicalstent and causes less arterial wall reaction. For application at sitesof small dissection after balloon angioplasty, a plaque tack of minimalfootprint may be used such as a single, thin ring-type tack with an L/Dratio in the range of 1/10 to 1/100.

Studies on stenting have shown that the length of a stent is correlatedwith a tendency for occlusion in multiple vascular territories. The morestent length that has been placed, the higher likelihood that thereconstruction will fail. The length of a stent is also directly linkedto the frequency and tendency of the stent to break when placed in thesuperficial femoral artery. The medical literature indicates that thesuperficial femoral artery performs like a rubber band, and it is likelythat changes to the natural elongation and contraction of thesuperficial femoral artery play a significant role in the failure modeof superficial femoral artery stents. In contrast, the small-profileplaque tack can be implanted only in local areas requiring their use,thereby enabling the blood vessel to retain its natural flexibility tomove and bend even after the surface has undergone tacking. Multipletacks may be implanted separated by regions free of metallic support,thereby leaving the artery free to bend more naturally.

Radial pressure exerted on the blood vessel wall can also besubstantially reduced by the small-profile tack design, even whenmultiple tacks are used in a spaced-apart configuration. To minimizethis outward force while still providing the required retention ofdissections against the arterial wall, a series of anchor barbs isutilized. The presence of the barbs applying focal pressure to the wallof the artery allows the rest of the tack to apply minimum outward forceto the artery wall. The points of the barbs which apply the pressure arevery focal, and this is where the most force is applied. The focalnature of the application of the pressure exerted by the tack alsominimizes the structural effects of the device. The uniformlydistributed focal anchor points provide a distribution of radial energymaximizing the tendency to form a circular lumen.

Another important parameter for design of a plaque tack is the ratio ofVessel Coverage Area (C) to Total Vessel Surface area (TVS). Thisequation can be applied to one tack device or when several spaced-aparttack devices are placed across the length of a blood vessel treatmentarea. For a plaque tack, the C/TVS ratio is in the range of about 60% orless, whereas for a stent it can be 100% or more (if applied to overlapthe treatment site). For a focal lesion, the conventional treated vessellength is X+10 mm to 20 mm where X is the length of the lesion and theadded length is adjoining on normal or less diseased artery. Intraditional stenting, the entire treated vessel length would be coveredwith a stent. For example, in the case of a 2 cm lesion, the treatedvessel length would be 3 to 4 cm (usually a single stent of this lengthwould be selected), so that C/TVS is 150%-200%. In contrast, with tackplacement, about ½ of X would be covered, and none of the adjoiningnormal or less diseased artery would be treated. For example, in a 2 cmlesion, approximately 1 cm would be covered, so that the C/TVS ratio isabout 60% or less. The key to this innovative approach is placement ofbands only in regions of dissections requiring arterial tacking.

In another preferred embodiment, a tack device is formed with concentricside rings or mesh bands connected by longitudinal bridge members. FIG.25 shows a detailed view of the preferred embodiment of the plaque tackformed with concentric rings on each side connected by a series ofbridging members. In the figure the concentric side rings are showncompressed for delivery in the blood vessel. When expanded, the diameterof the tack device is about equal to the width of the tack device. Thenumber of bridging members is chosen depending upon the application. Forexample, 6 or fewer bridge members may be used between the twoconcentric rings when desired for limiting neointimal hyperplasia.

The literature in the industry has noted that an important factor instent design may be the ratio of Relative Metal Surface Area (RMS)compared to the number of longitudinal segments in the device structure,for example, as presented by Mosseri M, Rozenman Y, Mereuta A, Hasin Y,Gotsman M., “New Indicator for Stent Covering Area”, in Catheterizationand Cardiovascular Diagnosis, 1998, v. 445, pp. 188-192. As adapted fromthe RMS measure, an equation for Effective Metallic Interface (EMI) maybe used to compare the embodiment of the tack device with longitudinalbridging members to a typical stent, as follows:

${EMI} = \frac{\left( {1 + n^{2}} \right)C}{\sum\limits_{s = 1}^{x}({lw})_{s}}$

where x is the number of sections of metal, l is an individual metalsection length, w is an individual metal section width, C is the vesselcoverage area underneath the device (lumen surface), and n is the numberof bridge members longitudinally connected between circumferentiallyoriented segments. The summation found in the denominator can beinterpreted as the total metal surface area. The embodiment of the tackdevice with longitudinal bridging members has an EMI≤10, whereas the EMIof a typical stent would be several times greater. This low EMI is dueto the nature of the tack design having a small foot-print and minimallongitudinal bridges while a stent typically has a large foot-print andwould be a multiple several times that.

FIG. 26 illustrates the use of multiple tack devices which are spacedapart over the length as compared to a treatment site compared to atypical stent. Preferably, the spacing between tack devices is at leastthe width of the tack device. Note that the spacing between adjacenttack devices leaves untreated vessel area. A typical stent is shown inthe upper part of the figure compared to the use of 6 spaced-apart tackdevices at the bottom part of the figure. The overall length oftreatment area is 6.6 cm (the same length of the stent) while each bandis shown as 6 mm long separated by 6 mm spaces. Therefore, the VesselCoverage Area for the stent is the same as Total Vessel Surface area(=6.6 cm×0.6π, or 12.44 cm²) which gives a C/TVS ratio of 100%. For theseries of spaced-apart tack devices, C is equal to 6×0.6 cm×0.6π, or6.78 cm², while TVS is 12.44 cm², therefore the C/TVS ratio is equal to54.5%.

When two or more stents need to be employed over an extended length oftreatment site, it has been a conventional practice to overlap adjoiningstents to prevent kinking between stents. Due to the increased metallattice, the region of overlap becomes highly rigid and noncompliant.This noncompliance limits the natural arterial flexibility and increasesthe tendency for restenosis. Stent fractures occur more frequently inthe superficial femoral artery where this bending has a high frequencyand are common when multiple stents are deployed and overlap. Stentfractures are associated with a higher risk of in-stent restenosis andre-occlusion. In contrast, the plaque tacks are designed to be appliedin local areas and not to be overlapped. Optimal spacing is a minimum of1 tack width apart for tacks. This permits the artery to maintain itsflexibility, and only a half or less of the treated length of the arterywill be covered with metal.

Another advantage of using the plaque tack is that the presence of itsouter barbs permits the pressure of tack upon the blood vessel wall tobe minimized by making the pressure focal and applying low pressurethrough the barb contact with the wall. The presence of the barbsapplying focal pressure to the wall of the artery allows the rest of thetack to apply minimum outward force to the artery wall. The uniformlydistributed focal anchor points provide a distribution of radial energymaximizing the tendency to form a circular lumen. Circular lumens offeradditional benefit from the standpoint of the vessel wall interaction,independent of the vascular injury.

Use of Plaque Tack after Drug Eluting. Balloon Angioplasty

The use of plaque tacks can be combined with use of Drug Eluting Balloon(DEB) angioplasty to manage post angioplasty dissection and avoid theneed for stents. In DEB angioplasty, a drug-eluting balloon or a drugcoated balloon is prepared in a conventional manner. The drug may beone, or a combination, of biologically active agents that are used forvarious functions, such as anti-thrombotic, anti-mitotic,anti-proliferative, anti-inflammatory, stimulative of healing, or otherfunctions. The DEB is delivered on a guidewire across an area ofblockage or narrowing in the blood vessel system. The DEB is inflated toa specific pressure and for a period of time consistent with themanufactures guidelines of use for treatment purposes, as it pertainsthe drug coating and the intended outcomes, then the DEB is deflated andremoved. At this stage the medication from the DEB has been transferredto the wall of the blood vessel. Intravascular imaging or ultrasound isthen used to assess the integrity of the artery and the smoothness ofthe blood vessel surface at the site where the balloon was inflated. Thepresence of damage along the surface may be indicated as dissection,elevation of plaque, disruption of tissue, irregularity of surface. Incases where the damage is focal or localized, the plaque tack may beused to tack down the damaged, disrupted, dissected, or irregular bloodvessel surface. This permits continuation of a ‘stent-free’ environmenteven if damage to the blood vessel has occurred after balloonangioplasty.

At this stage the medication from the DEB has been transferred to thewall of the blood vessel. Contrast is administered into the blood vesselunder fluoroscopic guidance or another method such as intravascularultrasound is used to assess the integrity of the artery and thesmoothness of the blood vessel surface at the site where the balloon wasinflated. In some cases, one or more of these completion studies willdemonstrate the presence of damage along the surface at the site of theballoon inflation. This damage may include dissection, elevation ofplaque, disruption of tissue, irregularity of surface.

The plaque tack delivery catheter is loaded with multiple tacks that maybe placed at the discretion of the operator, and advanced over aguidewire in the blood vessel to the location where the dissection ordisruption or irregularity has occurred. The location is specificallyand carefully identified using angiography. The plaque tack(s) is or aredeployed at the location(s) of the lesion. More than one tack may beplaced to tack down a major dissection. If more than one tack is placed,it may be placed only according to the rules of proper spacing of tacks.That is, the tack should be at least one tack-length apart and do notoverlap. After placement of the tack, it may be further expanded intothe wall of the blood vessel using a standard angioploasty balloon or adrug-eluting or drug coated balloon. The purpose of the tack is not somuch to hold the blood vessel lumen open as to tack down the non-smoothor dissected surface of the blood vessel. This ‘touch-up strategy’permits the resolution of the damage created by the drug-eluting or drugcoated balloon without resorting to stent placement and therebymaintaining a ‘stent-free’ environment.

As a further measure, described above, the plaque tack itself can beused to deliver medication to the blood vessel. In addition to thedelivery of medication from the barbs, the entire tack can be coatedwith medication prior to tack placement. The purpose of this activity isto permit the tack to elute biologically active agent or agents thathave positive effects on the blood vessel.

It is to be understood that many modifications and variations may bedevised given the above description of the principles of the invention.It is intended that all such modifications and variations be consideredas within the spirit and scope of this invention, as defined in thefollowing claims.

1.-20. (canceled)
 21. A method of treating a blood vessel comprising:advancing a delivery catheter loaded with multiple independentlydeployable self-expanding tacks to a treatment area defined by adissection in the blood vessel surface; independently deploying two ormore self-expanding tacks of the multiple independently deployableself-expanding tacks from the delivery catheter at the discretion of anoperator to treat the dissection in the blood vessel surface definingthe treatment area, such that a vessel coverage area (C) of the deployedtwo or more self-expanding tacks divided by a Total Vessel Surface Area(TVS) of the treatment area has a ratio (C/TVS) of less than or equal to60%, wherein the vessel coverage area is based on summation of an axiallength measured from a distal-most end to a proximal-most end for eachof the deployed two or more self-expanding tacks, and the Total VesselSurface Area is based on a distance from a distal-most end to aproximal-most end of the treatment area defined by the dissection in theblood vessel surface.
 22. The method of treating a blood vessel of claim21, wherein deploying two or more self-expanding tacks from the deliverycatheter further comprises deploying each self-expanding tack of the twoor more self-expanding tacks such that it does not overlap with anyadjacent tack of the two or more self-expanding tacks.
 23. The method oftreating a blood vessel of claim 21, wherein deploying two or moreself-expanding tacks from the delivery catheter further comprisesdeploying each self-expanding tack of the two or more self-expandingtacks spaced apart from any adjacent self-expanding tack of the two ormore self-expanding tacks by at least an axial length of aself-expanding tack of the two or more self-expanding tacks.
 24. Themethod of treating a blood vessel of claim 21, wherein a ratio of anaxial length to a diameter (L/D) for each self-expanding tack of themultiple independently deployable self-expanding tacks is equal to orless than
 1. 25. The method of treating a blood vessel of claim 21,further comprising engaging a wall of the blood vessel with at least oneof a barb and an anchor on each of the deployed two or moreself-expanding tacks of the multiple independently deployableself-expanding tacks to maintain a locking relationship between each ofthe deployed two or more self-expanding tacks and the wall of the bloodvessel.
 26. The method of treating a blood vessel of claim 25, whereinengaging the wall of the blood vessel further comprises piercing thewall of the blood vessel with the at least one of the barb and theanchor.
 27. The method of treating a blood vessel of claim 21, wherein aspacing of the deployed two or more self-expanding tacks in the bloodvessel is different than a spacing of the multiple independentlydeployable self-expanding tacks loaded in the delivery catheter.
 28. Themethod of treating a blood vessel of claim 21, wherein eachself-expanding tack of the multiple independently deployableself-expanding tacks comprises concentric rings connected by a series ofbridging members, and wherein independently deploying two or moreself-expanding tacks of the multiple independently deployableself-expanding tacks from the delivery catheter further comprisesself-expansion of the concentric rings.
 29. A method of treating a bloodvessel comprising: advancing a delivery catheter including multipleindependently deployable implants to a treatment area defined by adissection in the blood vessel surface; and deploying two or moreimplants of the multiple independently deployable implants from thedelivery catheter to treat the dissection in the blood vessel surface atthe treatment area, such that a vessel coverage area (C) of the deployedtwo or more implants divided by a Total Vessel Surface Area (TVS) of thetreatment area has a ratio (C/TVS) of less than or equal to 60%, whereinthe vessel coverage area is based on summation of an axial lengthmeasured from a distal-most end to a proximal-most end for each of thedeployed two or more implants, and the Total Vessel Surface Area isbased on a distance from a distal-most end to a proximal-most end of thetreatment area defined by the dissection in the blood vessel surface.30. The method of treating a blood vessel of claim 29, wherein deployingtwo or more implants from the delivery catheter further comprisesdeploying each implant of the two or more implants such that it does notoverlap with any adjacent implant of the two or more implants.
 31. Themethod of treating a blood vessel of claim 29, wherein deploying two ormore implants from the delivery catheter further comprises deployingeach implant of the two or more implants spaced apart from any adjacentimplant of the two or more implants by at least an axial length of animplant of the two or more implants.
 32. The method of treating a bloodvessel of claim 29, wherein deploying two or more implants from thedelivery catheter further comprises releasing two or more self-expandingimplants from the delivery catheter and allowing the two or moreself-expanding implants to self-expand.
 33. The method of treating ablood vessel of claim 29, further comprising positioning a balloon atthe treatment site and inflating the balloon to further expand thedeployed two or more implants.
 34. The method of treating a blood vesselof claim 29, wherein a ratio of an axial length to a diameter (L/D) foreach implant of the multiple independently deployable implants is equalto or less than
 1. 35. The method of treating a blood vessel of claim29, further comprising engaging a tissue of the blood vessel with atleast one of a barb and an anchor on each of the deployed two or moreimplants of the multiple independently deployable implants.
 36. Themethod of treating a blood vessel of claim 29, wherein a spacing of thedeployed two or more implants in the blood vessel is different than aspacing of the multiple independently deployable implants included withthe delivery catheter.
 37. A method of treating a blood vesselcomprising: advancing a delivery catheter having multiple implants toone or more dissections in a surface of the blood vessel; andindependently deploying two or more implants from the delivery catheterto treat a single dissection of the one or more dissections, such that avessel coverage area (C) of the deployed two or more implants divided bya Total Vessel Surface Area (TVS) of the single dissection has a ratio(C/TVS) of less than or equal to the ratio when the spacing betweenadjacent implants is at least the width of an implant of the multipleimplants, wherein the vessel coverage area is based on summation of anaxial length measured from a distal-most end to a proximal-most end foreach of the deployed two or more implants, and the Total Vessel SurfaceArea is based on a distance from a distal-most end to a proximal-mostend of the single dissection.
 38. The method of treating a blood vesselof claim 37, wherein deploying two or more implants from the deliverycatheter further comprises deploying each implant of the two or moreimplants such that it does not overlap with any adjacent implant of thetwo or more implants.
 39. The method of treating a blood vessel of claim37, wherein deploying two or more implants from the delivery catheterfurther comprises deploying each implant of the two or more implantsspaced apart from any adjacent implant of the two or more implants by atleast an axial length of an implant of the two or more implants.
 40. Themethod of treating a blood vessel of claim 37, wherein a spacing of thedeployed two or more implants in the blood vessel is different than aspacing of the multiple implants included with the delivery catheter.